A variety of capacitance type physical quantity sensors have been provided so far. The physical quantity sensors are configured as below. Movable mechanism parts such as a vibrator and a movable member are provided on a silicon substrate or a glass substrate by micromachining. Drive gaps are provided on a cap substrate at positions corresponding to the movable mechanism parts such as the vibrator and the movable member. These substrates are sealed by joining or bonding. The movable mechanism parts have sizes on the order of μm. Therefore, the influence of air resistance or the like leads to a problem of performance degradation. Thus, it is necessary to seal sensing portions at pressure atmospheres suitable for the movable mechanism parts such as the vibrator and the movable member.
The combined sensor has an acceleration sensor, an angular velocity and the like installed on the same substrate. Therefore, the acceleration sensor and the angular velocity sensor are sealed in such respective pressure atmospheres as to prevent their performances from being degraded. In general, the sensing portion of the acceleration sensor is sealed at atmospheric pressure and the sensing portion of the angular velocity sensor is sealed in a vacuum. Thus, the combined sensor free from performance degradation is provided.
The angular velocity sensor has the movable mechanism part which is a vibrator. In addition, when the vibrator is driven and vibrated at a given frequency, if it receives angular velocity, the Coriolis force occurs. The Coriolis force displaces the vibrator. Angular velocity is detected by detecting the displacement of the vibrator due to the Coriolis force. As the driving speed of the vibrator is faster, the Coriolis force becomes stronger. Therefore, to increase the detection sensitivity of the angular velocity sensor, it is necessary to vibrate the vibrator at high frequencies and at an amplitude of as large as several μm.
However, the vibrator fabricated by micromachining is formed at a minute gap; therefore, if driving atmosphere is at atmospheric pressure, the influence of the damping effect of air (sealing gas) is increased. This damping effect has an influence on the vibration of the angular velocity sensor at high frequencies and at large amplitude, which lowers the detection sensitivity of the angular velocity sensor. Accordingly, the angular velocity sensor capable of vibrating at high frequencies and at large amplitude can be provided by sealing the sensing portion of the angular velocity sensor in the atmosphere where the influence of the damping effect is small, that is, in a vacuum atmosphere.
On the other hand, the acceleration sensor has the movable mechanism part which is a movable member composed of a weight, a beam or the like. If acceleration is applied to the acceleration sensor, the movable member is displaced. The acceleration is detected by detecting the displacement of the movable member. If the acceleration sensor is sealed in the same vacuum atmosphere as is the angular velocity sensor, the movable member of the acceleration sensor has a reduced damping effect, which leads to a phenomenon in which the movable member continues to vibrate. In this case, high sensitivity acceleration detection by the acceleration sensor cannot be performed. Thus, the acceleration sensor is sealed in the atmosphere where the damping effect is large, i.e., in an atmospheric environment.
Patent Document 1 presents the following configuration as a publicly known example of a combined sensor combining an acceleration sensor with an angular velocity sensor. A through-hole (aeration path) is provided on an acceleration sensor side of a cap substrate sealing the acceleration sensor and the angular velocity sensor. The acceleration sensor and the angular velocity sensor are sealed in a vacuum and then a damping agent is filled via the aeration path. The through-hole is filled with solder, resin or the like. In this way, the acceleration sensor is sealed in the atmospheric environment and the angular velocity sensor is sealed in the vacuum atmosphere.
Patent Document 2 presents the following configuration. An acceleration sensor and an angular velocity sensor are sealed in an atmospheric pressure environment. Then, a cap substrate or a sensor substrate on the angular velocity sensor is bored with a through-hole. Thereafter, the through-hole is filled with silicon by Chemical Vapor Deposition (CVD). In this way, the angular velocity sensor is sealed at the pressure of CVD, i.e., in a vacuum atmosphere. In this method, the acceleration sensor is sealed in the atmospheric pressure environment and the angular velocity sensor is sealed in a vacuum atmosphere.